1. Field of the Invention
This invention relates to adhesive creep fixtures, and more particularly to an adhesive creep fixture configured to test adhesion properties in a plurality of loading modes for elements bonded to glass.
2. Description of Related Art
Adhesives are compounds that adhere or join two items together. Adhesives are extremely useful for many applications where penetrative fixation, such as screws or nails, is not feasible or desirable. Adhesives have become increasingly important in both the construction and automotive industries. One particular application where adhesives are used is adhering brackets to glass. This type of application commonly occurs with motor vehicle windows, where the glass window requires a linkage to the mechanism that lowers and raises the window.
In many instances when adhesive bonds are used to create fixation between two elements, characterizing the strength and durability of the bond created by the adhesive is desirable. This characterization becomes increasingly important for understanding the strength and durability of various compounds prior to utilizing a compound for a commercial application. Adhesive materials typically provide strength in tensile loading and shear loading. Tensile loading are types of loads that tend to pull the two bonded items apart. Shear loading are types of loads that tend to cause the two bonded items to slide relative to each other. Companies typically have test protocols in place to characterize adhesion strength of compounds in at least these two types of loading conditions.
Several solutions for testing the adhesive strength of materials have been proposed. U.S. Pat. No. 3,214,971 to Hammond et al., teaches a tester designed to measure the amount of tack an adhesive possesses. In Hammond, a patch of a tacky material, such as an adhesive, is positioned on a well within a carrier top. A probe attached to a variable speed motor is positioned in contact with the patch. The probe is attached to the motor via a carrier. A strain gauge is operatively attached to the carrier via a system of springs. When the motor is in operation, the carrier is drawn away from the patch until separation of the probe from the patch is achieved. The springs transfer the force required to separate the patch from the probe to the strain gauge.
In contrast, Japanese Patent Number JP 09-061340 to Yamagiwa teaches a method for testing a resin in shear. In Yamagiwa, a resin injection space defined by a U-shaped spacer is provided between the two items to be joined by the resin. The resin is subsequently injected into the resin injection space and hardened. A tensile tester clamps onto the materials and pulls the materials apart until fracture is achieved.
Adhesives also should be able to retain adhesion strength under various environmental conditions, such as exposure to moisture, extreme heat, or extreme cold. Adhesion testing under such harsh environmental conditions would allow the tester to understand how well the adhesive should perform when used in the real world. As such, having test fixtures capable of generating the tension and shear loads while being exposed to various environmental conditions is desirable.
Environmental chambers are laboratory test apparatus capable of tightly controlling and monitoring environmental conditions such as moisture and temperature. Environmental chambers are commonly utilized in industries where products are exposed to the elements. Environmental chambers are typically small, so the chambers generally do not have extensive space for the test articles. Therefore test equipment should be sized to fit and function within environmental chambers. Many conventional systems utilize large motorized devices that can cost tens to hundreds of thousands of dollars and are not typically capable of being exposed to environmental conditions.
Therefore, a need exists in the art for an inexpensive and reusable test apparatus capable of testing adhesive properties in multiple modes that may also be configured to perform while exposed to environmental conditions. The test apparatus should be able to be quickly switched from one test mode to another test mode. The test apparatus should be able to test actual components intended for use in commercial products. Further, the connection mechanisms between the test apparatus and the test parts should be able to isolate unintended forces from being transferred to the test parts.